The present invention relates to a phase shift adapter for an interferometer that supports a wavefront transmission element comprising a sphere or flat reference surface and precisely positions the element so that it can be translated parallel to the optic axis a distance on the order of an optical wave length and with an accuracy of a very small fraction of the wave length.
Fizeau interferometers have phase shifting structures for translation of wavefront transmission elements comprising reference flats or spheres through which an optical wavefront is transmitted. The sphere or flat can be loosely termed a lens, and will be called a lens or transmission element in this specification. These transmission elements have in the past been translated along the optical axis by three piezoelectric translators or actuators that are arranged symmetrically with respect to the optical axis. The translators and the electrical balancing networks needed for control are high priced and drive up the cost of the overall system.
A typical prior art interferometer system is the Mark IVxp made by Zygo. The present phase shift adapter will operate with such an interferometer using the standard bayonet mount that is present on the frame of the interferometer.
The present adapter thus can mount onto existing interferometers and provide the advantages of a mounting that can be translated axially accurately, easily and at overall lower cost, but which is very rigid in direction of unwanted movement.
The present invention relates to an output adapter for an interferometer that will mount a wavefront transmission element, comprising a flat or sphere for translatory movement along an optic axis. The adapter is a metal tube with a large center bore and a standard male bayonet on the end for attachment to the accessory bayonet mount of an interferometer. An accessory bayonet mount is provided on the opposite end for attachment of a wavefront transmission element, comprising a sphere or flat. The phase shift adapter thus installs between the interferometer bayonet and the transmission sphere or flat.
The body of the present phase shift adapter is a monolithic structure, and is separated into a fixed end support portion that mounts on the interferometer or frame and a movable end support portion for mounting the beam transmission element. The fixed end support portion and movable end support portion are connected by integrally formed flexure hinges. The two support portions are separated by gaps or slits formed in the monolithic structure by wire electrical discharge machining or similar machining. The flexure hinges also are formed by the same process, as well as by drilling holes where needed.
Four flexure hinges are arranged at the vertices of a parallelogram, nominally a rectangle, with the flexure hinges being formed by eight flexures defining four hinge links, one at each flexure hinge, as shown. The movable end support portion mounting the optical transmission element can be extended from the fixed end support portion in an optical axial direction of the optic wavefront by bending of the flexures and the rotation of the hinge links. All other motions are constrained by the relative rigidity of the fixed end support, and by the resistance of the flexure hinges to torsion and shear. A single piezoelectric translator or actuator is installed between the movable end support portion and the fixed end support portion, and the piezoelectric translator provides very precisely controlled axial motion of the movable end support portion. The flexure hinges act to restrain any motion of the movable end support portion other than axial motion, so only one piezoelectric translator or actuator is necessary.
The movable end support portion can be preloaded mechanically by compression springs acting in opposition to the piezoelectric translator to urge the movable end support toward the fixed end support of the phase shift adapter.
Another aspect of the present arrangement is mechanical damping of the movable end support portion by using plugs of an elastomeric material inserted or injected into holes drilled along a cut or gap that separates the two support portions and extends between the axially spaced flexure hinges on each side of the adapter.
The adapter does not require tilt and tip adjustment knobs that are common in most commercial interferometer bayonet mounts, in that the standard bayonet mount tilt and tip adjustments can be used.